1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device, in particular, applying a technology for forming a Silicon On Insulator (SOI) structure.
2. Related Art
A field effect transistor formed on an SOI structure has utility drawing attention in view of its easiness in element separation, latch-up free, small source-drain junction capacitance. In particular, since a complete depletion type SOI transistor can offer low power consumption and high operation speed and is easy to be driven with a low voltage, researches therefor are actively conducted.
As a method of manufacturing a semiconductor device having an SOI structure on a bulk wafer, for example, as described in T. Sakai et al., Second International SiGe Technology and Device Meeting, Meeting Abstract, pp. 230-231, May (2004), there is known a method of forming an SOI layer partially on a silicon substrate using a Separation by Bonding Si Islands (SBSI) method and then forming an SOI transistor in the SOI layer.
The method of forming the SOI structure using the SBSI method described above will be explained. Firstly, a silicon-germanium (SiGe) layer and a silicon (Si) layer are epitaxially grown sequentially on the silicon substrate, and then, a support member hole for supporting the silicon layer is formed. Subsequently, after forming thereon an oxide film and so on, patterning is executed thereon so as to obtain an element forming area and a form of the support member. After then, by selectively etching the silicon-germanium layer existing under the support member with hydrofluoric/nitric acid, the silicon layer is supported by the support member, and at the same time, a hollow section is formed under the silicon layer. Then, by growing oxide films respectively from the silicon substrate side and the silicon layer side using a thermal oxidation process on the hollow section, a buried oxide (BOX) layer is formed between the silicon substrate and the silicon layer. Further, after performing a planarization process on the silicon substrate, etching is performed thereon with an etching liquid such as hydrofluoric acid to expose the silicon layer on the surface, thereby forming the SOI structure on the silicon substrate.
Incidentally, in the forming method of the SOI structure described above, when the SiGe layer is epitaxially grown on the silicon substrate, there is a concern that a material gas for Ge adheres other sites then the desired site on the silicon substrate to cause SiGe to epitaxially grow on unnecessary sites such as side faces or the reverse side of the silicon substrate, thus exerting a harmful influence on the posterior process. Therefore, it is considered that prior to the process of epitaxially growing the SiGe layer, the entire surface of the silicon substrate is covered with a silicon dioxide (SiO2) film, then the silicon dioxide film is selectively removed from the desired site to expose the surface of the silicon substrate, and after then, Si and SiGe are epitaxially grown selectively on only this area. In this way, the problem that SiGe is epitaxially grown on other sites than the desired site on the silicon substrate can be prevented
However, if the state in which the silicon substrate is covered by the silicon dioxide film except the desired site is made, and the process proceeds while keeping the state, although the mechanism is not sufficiently figured out, the etching rate to the Si and Ge in SiGe is decreased in the process of selectively etching the SiGe layer described above with hydrofluoric/nitric acid, thus formation of the hollow section preferably penetrating therethrough under the silicon layer is sometimes failed.